Is Clearwire the savior of global LTE?

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Clearwire is moving full-speed ahead with a flavor of LTE that is uncommon in the US, but used heavily overseas. Interoperability is high on its list of priorities, though: the company is spearheading the effort to promote multi-mode chipsets.

Two types of LTE currently exist: FDD (frequency division duplex) and TDD (time division duplex). FDD-LTE uses two separate frequency ranges for uplink and downlink, while TDD-LTE uses a single range of frequencies. Worldwide, TDD-LTE seems to have a good deal more traction, however here in the US FDD-LTE has so far been the mode of choice.

China Mobile, India’s Bharti Airtel, and Japan’s Softbank are either planning or have deployed TDD-LTE. In Europe, the technology has supporters in Sweden’s Hi3G (which plans a dual-mode network), and UK Broadband, who recently switched on its own TDD-LTE network in the London borough of Southwark.

So far Clearwire is the only US operator to move forward with TDD-LTE. That said, it must consider the reality of the US market if it hopes to strike agreements with other carriers. Major partner Sprint is moving towards LTE (and will likely want some capacity), and MetroPCS has expressed interest in buying capacity on Clearwire’s network. These carriers use FDD-LTE, so any device currently available on these networks will be incompatible with Clearwire’s.

With a vested business interest in somehow solving this problem, Clearwire is announcing agreements with major chipmakers to develop and promote dual-mode (FDD+TDD) chips. Sequans penned a deal with Clearwire on Monday, and Qualcomm signed a deal on Tuesday. The partnership with Qualcomm is especially significant, considering the company supplies a significant portion of the cellular chipsets in use today. Dual-mode chips are expected to debut by the end of this year.

This is good news, but before you get too excited, consider these caveats. Clearwire says its LTE network will not be available until the first half of 2013 at the earliest. Only Bharti Airtel and UK Broadband have launched TDD-LTE commercially worldwide, and other European operators are just now in the planning stages. This means widespread TDD-LTE deployment is likely several years away.

Then you must consider the issue of frequencies. As many as 38 difference frequency ranges may be used for LTE worldwide by 2015, a study from Wireless Intelligence predicts. That’s a heck of a lot of fragmentation, and there’s almost no possible way manufacturers will be able to squeeze support for all those frequencies onto one chip.

“Every country in the world will have at least one TDD network and several FDD networks. The major problem lies in the frequencies being used in each country for the networks,” ExtremeTech’s wireless analyst Neal Gompa explains. “TDD-LTE is not going to be the roaming savior that Clearwire’s deluded CEO [Erik Prusch] hopes it to be.”

CDMA won globally. The UMTS standards chose NTT DoCoMo’s W-CDMA technology for the air interface for 3G, which evolved separately from Qualcomm’s development of CDMA2000 from cdmaOne. What people refer to as TDMA was Motorola’s AMPS and D-AMPS technologies. Those are in the same class as iDEN and GSM as 2G technologies. Incidentally, they all used FD/TDMA (frequency division/time division multiple access) as the basic air interface.

“Every country in the world will have at least one TDD network and several FDD networks. The major problem lies in the frequencies being used in each country for the networks,” ExtremeTech’s wireless analyst Neal Gompa explains. “TDD-LTE is not going to be the roaming savior that Clearwire’s deluded CEO [Erik Prusch] hopes it to be.”
We read an entire story about breakthroughs in compatibility but the last sentence is a scoffing and unexplained sneer? Are there some sour grapes here?

Nobody is using the same frequencies, even on TDD. There’s at least four different incompatible TDD frequencies. AFAIK, you can only have one TDD frequency, two FDD high band frequencies, and two low band FDD frequencies (or three FDD high band frequencies and two FDD low band frequencies).